The following description is provided to assist the understanding of the reader. None of the information provided or references cited is admitted to be prior art to the present technology.
Redox flow devices are electrochemical systems wherein the oxidation and reduction of two different chemical species (ions) from cathodic and anodic solutions take place on inert electrodes (current collectors). In redox flow batteries, energy is stored and released through a reversible electrochemical reaction between two electrolytes which are separated by ion-conductive membrane, and contain dissolved redox-active ions. The cathodic and anodic electrolytes are stored externally to the battery and circulated through the cell(s) of the reactor on opposite sides of an ionically transporting membrane. Flow batteries can be rechargeable and their energy capacity is typically determined by the mass of the electroactive materials, i.e. limited by solvability of redox ions and the amount of the electrolyte in storage tanks.
Because of the large scale energy storage capacity and low energy density, redox flow devices and batteries are conventionally used in stationary applications, e.g. with renewable energy systems such as solar cells and wind power. However, conventional redox flow batteries tend to have low energy densities due to the limited solubility of the redox salts that are typically employed and have relatively poor energy-to-volume ratio. There is, therefore, a need for redox flow devices and flowable redox materials which have high energy density per volume so that they can be used in portable or mobile applications such as transportation, portable military devices, local grid leveling, communication devices, and the like.